January 23, 2007

Dinosaur May Have Resembled the Biplane

by ssavage

WASHINGTON -- When the Wright Brothers first took to the sky in a biplane, they were using a design nature may have tried 125 million years earlier. A new study of one of the earliest feathered dinosaurs suggests it may have had upper and lower sets of wings, much like the biplanes of early aviation. Today, the biplane is widely considered an old-fashioned rarity.

And the design is no longer seen in birds, though it's not clear if it was a step on the way to modern birds or a dead end, tested by nature and discarded.

The intriguing possibility of a biplane dinosaur - Microraptor gui - is suggested by Sankar Chatterjee of Texas Tech University in this week's online issue of Proceedings of the National Academy of Sciences.

Microraptor was described by Xing Xu of the Chinese Academy of Sciences in 2003 as having aerodynamic feathers on both its arms and legs. Xu suggested at the time that it glided, extending its legs backward so its wings were arranged one behind the other, like a dragonfly.

But that would be aerodynamically inefficient for a feathered creature, Chatterjee concluded, noting that the feathers on the legs would not face forward.

Instead, he suggested, the legs of the two-pound creature could have been held below the body in flight, creating two staggered wing sections, the upper one slightly ahead of the lower one.

One other flying dinosaur, Pedopenna, also had feathers on its legs, Chatterjee said, and modern raptors such as falcons have short feathers on their upper legs which reduce air resistance as they fly.

"Aircraft designers have mimicked many of nature's flight 'inventions,' usually inadvertently," Chatterjee wrote. "Now, it seems likely that Microraptor invented the biplane 125 million years before the Wright 1903 Flyer."

Xu, who said a variety of reconstructions have been suggested since the original one, called Chatterjee's proposal "likely," but added that "we really need to work painstakingly to check all details and have an accurate reconstruction, and then we can compare different models in computer or even in wind tunnel, which we are planning to do."

"Microraptor is a critical species in understanding the origin of flight," added Xu, who was not associated with Chatterjee's research team.

Matthew Carrano, curator of dinosaurs at the Smithsonian's National Museum of Natural History, said the question focuses on what the legs can do, and it's a difficult problem because the fossils are flat and require interpretation as to what they would have looked like in three dimensions.

Carrano, who also was not part of Chatterjee's research team, said this creature was probably a side branch rather than a stage evolution had to pass through on the way to today's birds.

"It's difficult to see how this animal does anything well, it seems so ungainly," Carrano said. "It forces us to think creatively because it's so far off the beaten path."

There are often such experiments that fall by the wayside, he said.

"The important thing is, because we've now got all these feathered dinosaurs to look at, it has kind of opened the gates a bit to speculating about how flight evolved," Carrano said.